NYC is very hot and stuffy in the summer, but also has a lot of shade. A large part of this shade comes from large buildings, but most blocks have trees and there are some notable parks with a lot of tree cover as well. I get bitten all the time in the park when not in direct sunlight, but not so much when I'm downtown with the same level of shade.
I wondered if there was something to this natural shade (from trees) vs artificial shade (from buildings), or if the park in general was just more conducive to mosquito growth.
I also added cute little PLA 3D Printed frogs as another factor in my experiment to see if they would have any effect on the data. I predicted they might have either a positive effect on the number of mosquitoes due to the additional surface area for mosquitoes to oviposit, or a negative effect due to mosquitoes identifying the frogs as natural predators (scare frogs) and staying away from the trap.
This left me with 6 treatments: No Shade & No Frog, No Shade & Frog, Artificial Shade & No Frog, Artificial Shade & Frog, Natural Shade & No Frog, Natural Shade & Frog
Each trap was identical to help keep the experiment controlled and consisted of a 16 ounce red plastic cup, 1.5 cups of tap water, 0.5 Tsp of fish food, and a third of a paint stirring stick. I made them all at once in an assembly line like fashion.
I set up each pair of traps in my landlord's backyard and checked in every five days.
After the first five days only the Artificial Shade No Frog Trap had larvae, 35, and I identified them to be Culex due to the egg rafts in the cup as well as their long siphons. There were also a lot of these tiny white slug things in most of my traps, which I've noticed a lot of other people's blogs mentioning as well. I've noticed the white slugs seem to enjoy eating or attacking the egg rafts in some way, which was pretty interesting.
After the next cycle more of my traps had larvae. Natural Shade No Frog, Artificial Shade No Frog, and Natural Shade With Frog all had larvae and are ordered in least to greatest in terms of number of larvae. There were too many to count so I eyeballed the rankings, but I took a half ounce sample of each and they confirmed ranking above. The No Shade traps continued to be free of mosquitoes, but they did contain a few brave white slugs.
All of the mosquitoes were Culex, and there were numerous egg rafts in each of the traps. I found one early pupae and also discovered that the white slugs are somehow immune to the isopropyl alcohol that kills the mosquito larvae.
After the second cycle I was going out of town for a little over a week, so in order to not release a couple hundred mosquitoes I emptied and washed out all of my traps.
When I got back I restarted the experiment, and five days later I analyzed the traps. The Artificial Shade No Frog trap was brimming with larvae and tons of egg rafts, and the Natural Shade With Frog trap also had larvae, though much less. With the exception of the No Shade traps, all other traps contained egg rafts and white slugs.
I will be continuing to monitor the traps every five days. As of now its pretty clear that mosquitoes will not oviposit in water exposed to direct sunlight (frog or not) but I don't have enough data to detect any further relationship between my three variables: No Shade, Natural Shade, and Artificial Shade. The frogs appeared to have no effect on oviposition rates when compared to their No Frog trap counterparts. I do not believe they will have a place in the future of mosquito population control.
That being said, I think the fact that Culex mosquitoes lay all of their eggs in a single go may make the results of the entire experiment unreliable. Rather than a single larvae representing the preference of a single ovipositing female mosquito (like with the Aedes species), in this case larvae are batched together in groups of over one hundred based on wherever their mother decided to go. This means rather than a trap containing 100+ data points, it really only contains one or two. I think this may be the reason why my data is so inconclusive, as rather than a thousand-ish data points overall, I really only have around 7, and with a sample size that low, sampling variability takes over everything. I bet that in an environment with primarily Aedes mosquitoes an experimental design similar to this one would probably work a lot better.
About the author: Benjamin is a senior from Brooklyn, NY. This blog describes a mosquito trapping experiment conducted as part of the NASA STEM Enhancement in the Earth Sciences (SEES) summer high school research internship. His virtual internship is part of a collaboration between the Institute for Global Environmental Strategies (IGES) and the NASA Texas Space Grant Consortium (TSGC) to extend the TSGC Summer Enhancement in Earth Science (SEES) internship for US high school (http://www.tsgc.utexas.edu/sees-internship/). Benjamin shared his experience this summer in this blog post.
